1. Field of the Invention
This invention relates to domino logic circuits and, more specifically, to such circuits which are selectively precharged.
2. Brief Description of the Prior Art
Domino logic circuits are well known in the art and generally include in series between a source of power and reference voltage, a first transistor of one of n-channel or p-channel and preferably p-channel, one or more serially connected second transistors of the other of n-channel or p-channel and a third transistor of the same type as the second transistor(s). An output is taken from the node at the junction of the first transistor and second transistor(s) and inverted by an inverter. During the precharge operation, the first transistor is normally conducting and the second and third transistors are normally non-conducting to provide a high signal at the precharge node at the junction of the first transistor and second transistor(s) and a low signal at the inverter output, this being the precharging phase of operation. If the second and third transistors are all then concurrently activated and the first transistor is deactivated, the voltage at the node at the junctions of the first transistor and second transistor(s) will go low whereas that node will remain high if any of second or third transistors is not activated after precharge. The output of the inverter is the inverse of the voltage at the node. It is therefore apparent that the voltage at the precharge node will not change appreciably if any of the one or more second transistors are not activated in the cycle prior to the next precharge.
Domino logic circuits are generally used in circuitry containing many such circuits, such as, for example, in matrix arrangements or the like wherein only one of plural such logic circuits will be activated at any one time with the other logic circuit being unactivated. It follows that power is wasted whenever a precharge voltage is applied to the precharge node of a logic circuit which has not been activated when the precharge node is already at the high voltage.